Wheel motors and pumps for vehicles, hydraulic drive systems, systems using accumulators for regenerative braking and acceleration, and methods of casting cylinders made of a first material within a second material are known. The following references relate to the above listed subject matter.
U.S. Pat. Nos. 4,883,141 and 5,000,282 to Walker disclose hydraulic wheel motor and pump units for use with a pair of mechanically and a pair of non-mechanically driven wheels, respectively, to modify a two-wheel drive vehicle into a four-wheel drive vehicle. The flow of fluid into and out of cylinders of the hydraulic units are controlled by timing valve assemblies which are separate from piston assemblies reciprocating within the cylinders. The cylinders are housed within machined castings which are affixed to the vehicle. Further, seals are provided between the cylinders and piston assemblies to prevent leakage from the hydraulic units.
A number of patents show hydraulic vehicle drive systems having fluid accumulators for storing energy during vehicle deceleration and using the stored energy to assist in vehicle acceleration. These systems typically input and output energy relative to accumulators by way of vehicle drivetrains. Examples include U.S. Pat. Nos. 4,813,510, 4,745,745, 4,387,783, 4,350,220, and 4,215,545.
Rohde, U.S. Pat. No. 4,663,935, discloses an energy storage and retrieval system for a vehicle. A hydraulic pump/motor device, connected with a hub portion of a wheel, uses pressurized hydraulic fluid which is stored in a tire portion of the wheel. The system is confined to use with a single tire and wheel.
A number patents describe cylinders made of a first high strength material being cast within a second lower strength material. Examples of this type of casting procedure may be found in U.S. Pat. Nos. 5,005,469, 4,872,396, and 3,069,209. However, none show hydraulic wheel motors or pumps.